1. Field of the Invention
This invention relates to improvements in a track guide bearing assembly wherein a number of balls are disposed between an axial ball rolling groove provided in a track shaft and an axial ball rolling groove provided in a slide table, and these balls can circulate along a ball circulating path provided in the slide table.
2. Description of the Prior Art
Such a track guide bearing assembly has a great load capacity because the balls are adapted to roll while fitting in an axial concave groove, and has the advantage that the slide table can be moved easily through a rather large distance because the balls circulate, and thus such an assembly has often been used as the guide element of a machine tool, a measuring instrument or the like.
However, the track guide bearing assemblies according to the prior art have been of such a construction that the circulation of balls may not always be as smooth as desired, or the number of steps in working or assembling the various parts may be rather great.
That is, many of the track guide bearings according of the prior art, as shown for example in FIG. 4 of the accompanying drawings, have suffered from the disadvantage that the balls 5 fitted in the ball rolling groove 2 of a track shaft 1 and the ball rolling groove 4 of a slide table 3 must be directed into an arcuate ball path 7 formed in a side plate 6 to circulate the balls 5. In order to direct the balls in this circulating path 7, a tongue 9 formed in a retainer 8 is bent so as to become proximate to the ball rolling groove 2 and therefore the balls 5 strike against the tongue 9 of the retainer during their travel end may not circulate smoothly.
Another type of track guide bearings shown in FIG. 5 of the accompanying drawings has a projection 19 adapted to extend into the ball rolling groove 2 of a track shaft 1 is formed on a portion of a side plate 16, and again in this track guide bearing, as in the track guide bearing of FIG. 4, the balls 5 may strike against a corner of the projection 19 and, therefore, the circulation of the balls entering an arcuate ball path 17 may not always be smooth.
In a track guide bearing shown in FIG. 6 of the accompanying drawings, the circulation of the balls of the above-described prior art track guide bearings has been improved. In this track guide bearing, balls 5 fitting in the ball rolling groove 4 of a slide bed 3 are retained by a sheet-like retainer 18 extending over the outside of the balls over the length of the groove 4, and an escape groove 20 for receiving the retainer 18 is formed at the bottom of the groove 12 of a track is formed in the ball rolling groove 12 of a track shaft 11. The end of this retainer 18 is formed into an arcuate portion having the same radius as the arc of the arcuate ball circulating path 27 of a side plate 26 and the retainer 18 is fixed to the side plate 26 by a pin 21 fitted in a square groove formed in the side plate 26.
The track guide bearing of FIG. 6 has the advantage that the balls 5 smoothly circulate while being guided by the retainer 18 as they enter the circulating path 27. However, this track guide bearing has suffered from the disadvantage that the retainer thereof is high in working cost and the attachment thereof to the side plate is cumbersome.